In 1995 the OECD's Centre for Educational Research and Innovation (CERI) published the first set of comparable data in the field of special needs education. This work strengthened the view that a different comparative framework would need to be developed if reliable and valid comparisons were to be made. In 1996 the first discussions began with countries on developing a resource-based definition. This would help to overcome different national interpretations of concepts such as special educational needs which cover very different populations of students experiencing difficulties in accessing the curriculum.
For policy relevant comparisons to emerge, this approach would also require that the students included under this definition would need to be subdivided into some form of straightforward classification scheme. Countries agreed on a tri-partite system in which students are divided into three cross-national categories, A, B and C.
Three data collection rounds have taken place, in 1999, 2001 and 2003. 27 member countries, or regions of member countries have participated to this exercise.
The analysis of these data have been published in a series of monographs.